The OEM BMW skid plates are super robust, they just hang really low.
I have a buddy that has the oem one and he has hit some pretty gnarly stuff without issue, but he would hit less stuff if his plate sat closer to the pan like the one you made.
I need to build a plate for my E30 too. I've been looking at a few on E30tech and R3V for ideas, but this is probably one of the better ones I've seen.
I would just steal your plans, but I have an S50 in mine, so the pan sits a little lower.